1. Field of the Invention
The present invention relates to a hybrid working machine using both engine power and electric power.
2. Description of the Related Art
THE RELATED ART will be described taking an excavator of a preferred example of the present invention as an example.
The excavator is, as shown in FIG. 6, formed by rotatably mounting an upper rotating body 2 on a crawler type lower traveling body 1 and attaching a working attachment 3 to the upper rotating body 2.
The working attachment 3 is formed by a boom 4 capable of raising and lowering, an arm 5 attached to an end of the boom 4, a bucket 6 attached to an end of the arm 5, a boom cylinder 7, an arm cylinder 8 and a bucket cylinder 9 serving as hydraulic actuators for driving the boom, the arm and the bucket.
As an actuator for rotating the upper rotating body 2, a hydraulic motor is used in the case of a hydraulic excavator, and a rotation motor serving as an electric actuator is used in the case of a hybrid excavator.
In the hybrid excavator, there is a known hybrid excavator having a so called parallel type drive mode (refer to Japanese Patent Laid-Open No. Hei11-13548).
In the above type, a hydraulic pump and a generator motor for performing a generator operation and a motor operation are connected to an engine serving as a common power source in parallel so as to drive a hydraulic actuator by the hydraulic pump, and meanwhile to drive a rotation generator by the generator operation of the generator motor or an electric storage device.
The electric storage device is electrically charged by a generator action of the generator motor. The generator motor timely performs a motor action by discharge power of the electric storage device so as to assist the engine.
Meanwhile, rotation speed of the engine is controlled by operating accelerator operating means and hence changing a governor position (a fuel injection amount), and in general, a power generation amount of the generator motor is changed in accordance with the governor position and a load level (refer to Japanese Patent Laid-Open No. 2004-150305).
It should be noted that as a method for controlling the rotation speed of the engine, there is a general method for controlling and making actual rotation speed of the engine to be target rotation speed in relation to an accelerator operation amount (governor position) on the basis of the time of no load, and changing the rotation speed of the engine in accordance with a governor characteristic at the time of load imposed. However, there is sometimes a case where the actual rotation speed of the engine is controlled so as to correspond to the target rotation speed irrespective of the load (refer to Japanese Patent Laid-Open No. 2001-12259).
In the above hybrid excavator, at the time of operating the generator of the generator motor (at the time of electrically charging the electric storage device), even if the operation is stopped, there is a state that the load is imposed on the engine by the generator action.
Therefore, in the case where an accelerating operation of the engine is performed in the above state, it is not possible to use torque which is sufficient for accelerating the engine and hence it takes time for the acceleration.
Moreover, by the accelerating operation, control for increasing a power generation amount in accordance with the governor position is performed as mentioned above. Therefore, the rotation speed of the engine is not increased while the engine load is further increased. As a result, there is a possibility that the engine cannot be accelerated or engine failure is caused.